Image sensors, such as charge-coupled device (CCD) image sensors or complementary metal oxide semiconductor (CMOS) image sensors, incorporated in imaging apparatuses including digital cameras convert light received through a color filter to electrical signals by photoelectric conversion, and output the electrical signals as pixel signals. Such color filters include a RGB color filter, on which red, green, and blue patterns are formed, or a YMCK color filter, on which yellow, magenta, cyan, and black patterns are formed. A single-chip image sensor outputs a pixel signal of one color for one pixel. When using the RGB color filter, the image sensor outputs a pixel signal representing one of red (R), green (G), and blue (B) color components for one pixel.
Each pixel signal output from the single-chip color image sensor needs interpolation to generate pixel signals representing the other color components. Such interpolation may be performed using various algorithms. For example, one interpolation method calculates the degree of correlation in the horizontal direction and the degree of correlation in the vertical direction, and uses a pixel located in the direction with a higher correlation to perform pixel interpolation. Another interpolation method may perform weighting in accordance with the distance between a target pixel and its neighboring pixel before such pixel interpolation.
A technique described in Patent Literature 1 (Patent Literature 1: Japanese Unexamined Patent Publication No 2006-186965) differentiates a gray area and a color area in an image obtained by an image sensor with a Bayer array (RGB color filter), and performs pixel interpolation in accordance with the characteristics of the image areas. In particular, the technique in Patent Literature 1 reduces false colors in an area of boundary between a gray area and a color area. For the area of boundary between the gray area and the color area, the technique in Patent Literature 1 determines the direction of correlation with a method intended for a grayscale image area, and performs pixel interpolation with an interpolation method intended for a color image area, thus reducing false colors caused by pixel interpolation.